The present invention relates to the art of electrochemical cells, and more particularly, to a new and improved header insulator for an electrochemical cell used in implantable medical devices. Further, the present invention relates to an electrochemical cell comprising the novel header insulator and a method of providing an electrochemical cell incorporating the same.
Present battery designs typically include several insulators assembled to the inside of a battery header. First, the terminal ferrule for case conductive designs is usually provided with an insulator that serves two primary functions. The insulator electrically insulates the terminal ferrule and the feed-through pin from the internal electrodes of the battery. Also, it isolates the glass to metal seal and prevents leakage of electrolyte.
Second, an insulating strap type insulator is typically disposed adjacent to the interior surface of the header in order to electrically insulate the internal surface of the header from the internal electrodes of the battery to prevent short circuits.
Third, a welding shield provides thermal insulation between the header and the internal battery components (in particular the separator) when the header is welded to the top of the battery case.
Finally, the fill ferrule is also usually provided with an insulator that serves a couple of functions. It electrically insulates the fill ferrule from the internal electrodes of the battery, and it thermally insulates the fill ferrule from other internal battery components, particularly the separator, when the final close weld is conducted.
Each of the individual insulators adds to the manufacturing costs and adds to the steps required for assembly. Accordingly, what is needed is a unitary header insulator that meets all of the electric and thermal insulation requirements of the above-described insulators and that facilitates alignment of the battery electrodes within the case.
The present invention meets the above-described needs by providing a header insulator that is preferably manufactured from a material with properties for electrical and thermal insulation and that is formed as a unitary member having a plurality of integrally formed bosses. The header insulator provides a terminal ferrule boss, a fill ferrule boss, and at least one additional boss for maintaining the alignment of the battery electrodes.
The present invention is disposed between the lid of an electrochemical cell and the electrode assembly. In a typical electrochemical cell, the electrode assembly has terminal leads extending from the anode electrode and the cathode electrode such that positive and negative terminals are created for attachment to an external circuit. In a xe2x80x9ccase negativexe2x80x9d configuration, the anode electrode is connected to the case serving as the negative terminal. A feed-through pin establishes the positive terminal and is connected to the cathode electrode through an opening in the lid. The inside of the opening is a glass insulator that keeps the cathode electrically isolated from the case.
The present invention provides a header insulator with a first boss capable of registering with the terminal ferrule such that it is electrically and thermally insulated from the electrode assembly. A second boss on the opposite side of the insulator provides for thermal and electrical insulation of the fill ferrule from the remainder of the electrode assembly. Additional bosses are disposed along the length of the insulator and extend downward into the case such that the electrode assembly is prevented from becoming misaligned. If the electrodes become misaligned, the performance of the battery is degraded.
The design of the present invention is advantageous for several reasons. First, substitution of a single insulating member for several insulating members reduces the costs associated with manufacturing due to fewer parts and easier assembly. Second, the additional bosses on the header insulator maintain alignment of the electrode assembly such that discharge performance is not degraded by misalignment of the anode and cathode electrodes. The additional bosses are advantageously equipped with openings to prevent isolated build-up of electrolyte that could lead to decreased battery performance.
Other objects, features, and advantages of the present invention will become apparent upon reading the following detailed description of embodiments of the invention, when taken in conjunction with the accompanying drawings and the appended claims.